Sheet feeding device and image forming apparatus having same

ABSTRACT

A sheet feeding device includes first and second sheet feeding stocker provided in a main body and placed side by side in a horizontal direction, in which sheets are taken out from the first sheet feeding stocker and conveyed through a horizontal conveyance unit provided above the second sheet feeding stocker. The respective first and second sheet feeding stockers can independently be pulled out forward from the main body in a direction intersecting with a sheet conveying direction in the horizontal conveyance unit. The sheet feeding device includes an engaging mechanism for engaging the horizontal conveyance unit and the first sheet feeding stocker so that the first sheet feeding stocker is pulled out integrally with the horizontal conveyance unit when the horizontal conveyance unit is pulled out forward from the main body.

This application is based on an application No. 2009-213298 filed in Japan on Sep. 15, 2009, the entire content of which is hereby incorporated by reference.

TECHNICAL FIELD

The invention relates to a sheet feeding device, and more specifically relates to a sheet feeding device including two sheet feeding stockers placed side by side in left and right directions, in which sheets are taken out from one sheet feeding stocker and conveyed through a horizontal conveying path provided above the other sheet feeding stocker for paper feed operation.

The invention also relates to an image forming apparatus having such a paper feeding device.

BACKGROUND ART

One example of conventional image forming apparatuses having a sheet feeding device of this kind has been disclosed in JP H05-097262 A. The sheet feeding device includes two sheet feeding stockers (decks) placed side by side in right and left directions below an image forming apparatus main body, in which sheets (paper sheets) are taken from a left-side feed stocker by a pickup roller provided in the upper part thereof, conveyed to the right direction through a horizontal conveying path provided above a right-side sheet feeding stocker, and then fed upward through a longitudinal conveying path. The sheets stocked in the right-side sheet feeding stocker is taken out by the pickup roller provided above the sheet feeding stocker, and fed upward through the longitudinal conveying path.

These two sheet feeding stockers can be pulled from the main body in directions intersecting with the respective feeding directions. The member constituting the horizontal conveying path (referred to as “horizontal conveyance unit”) can also be pulled from the main body in a manner independent of the two sheet feeding stockers in a direction intersecting with the feeding direction. With this configuration, users can easily remove jammed sheets by respectively pulling the two sheet feeding stockers and the horizontal conveyance unit at the time of jamming relating to paper feeding operation.

SUMMARY OF THE INVENTION Technical Problem

However, in the above configuration, the two sheet feeding stockers and the horizontal conveyance unit can be pulled out independently, and therefore when a sheet stops at a position lapping over both the left-side sheet feeding stocker and the horizontal conveyance unit at the time of jamming relating to paper feed operation, sheet tear (so-called “tearing separation”) may occur if users pull out only the horizontal conveyance unit, for example, from the main body.

Accordingly, an object of the present invention is to provide a sheet feeding device which enables users to easily remove jammed sheets while preventing sheet tear at the time of jamming relating to paper feed operation.

Another object of the present invention is to provide an image forming apparatus having such a sheet feeding device.

Solution to Problem

In order to accomplish the above object, a sheet feeding device in one aspect of the present invention, comprising:

first and second sheet feeding stockers provided in a main body and placed side by side in a horizontal direction, wherein

sheets are taken out from the first sheet feeding stocker and conveyed through a horizontal conveyance unit provided above the second sheet feeding stocker, wherein

the respective first and second sheet feeding stockers can independently be pulled out forward from the main body in a direction intersecting with a sheet conveying direction in the horizontal conveyance unit, and wherein

an engaging mechanism is provided for engaging the horizontal conveyance unit and the first sheet feeding stocker so that the first sheet feeding stocker is pulled out integrally with the horizontal conveyance unit when the horizontal conveyance unit is pulled out forward from the main body.

An image forming apparatus in one aspect of the present invention is an image forming apparatus having the sheet feeding device.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

FIG. 1 is a front view showing an entire image forming apparatus having a sheet feeding device in one embodiment of the invention;

FIG. 2 is a cross sectional view showing the schematic configuration of the image forming apparatus;

FIG. 3 is a front view showing the layout of left-side and right-side sheet feeding stockers and a horizontal conveyance unit of the sheet feeding device;

FIG. 4 is a perspective view showing a protrusion as an engaging mechanism provided in the horizontal conveyance unit of the sheet feeding device;

FIG. 5 is a front view showing a protrusion as a locking mechanism provided in a conveyance door of the sheet feeding device;

FIG. 6 is a perspective view showing the protrusion as a locking mechanism provided in the conveyance door of the sheet feeding device corresponding to FIG. 5;

FIG. 7 is a front view showing the locking mechanism in an unlocked state;

FIG. 8 is a perspective view showing the locking mechanism in an unlocked state corresponding to FIG. 7;

FIG. 9A is a plan view showing the left-side and right-side sheet feeding stockers and the horizontal conveyance unit of the sheet feeding device in the state of being housed in the main body;

FIG. 9B is a plan view showing the horizontal conveyance unit of the sheet feeding device in the state of being pulled out from the main body together with the left-side sheet feeding stocker;

FIG. 10 is a perspective view showing the left-side and right-side sheet feeding stockers and the horizontal conveyance unit of the sheet feeding device in the state of being housed in the main body;

FIG. 11 is a perspective view showing the left-side sheet feeding stocker of the sheet feeding device in the state of being pulled out from the main body;

FIG. 12 is a perspective view showing the right-side sheet feeding stocker of the sheet feeding device in the state of being pulled out from the main body; and

FIG. 13 is a perspective view showing the horizontal conveyance unit of the sheet feeding device in the state of being pulled out from the main body together with the left-side sheet feeding stocker.

DESCRIPTION OF EMBODIMENTS

FIG. 1 shows an entire image forming apparatus (designated by reference sign 100) of a color tandem system having a sheet feeding device in one embodiment of the invention seen from the front side. FIG. 2 shows a schematic sectional configuration of the image forming apparatus 100. As shown in FIG. 2, the image forming apparatus 100 includes an intermediate transfer belt 108 as an annular image carrier provided generally in the center inside a main body casing 101, the intermediate transfer belt 108 being wound around two rollers 102 and 106 and moving in the circumferential direction. One roller 102 out of two rollers 102 and 106 is placed on the left-hand side in the drawing, while the other roller 106 is placed on the right-hand side in the drawing. The intermediate transfer belt 108 is supported on these rollers 102 and 106, and is rotated in an arrow X direction.

Toner containers 128Y, 128M, 128C and 128K for storing respective color toners of yellow (Y), magenta (M), cyan (C) and black (K) are placed side by side in order from the left-hand side in the drawing above the intermediate transfer belt 108. These toners are respectively fed from the toner containers 128Y, 128M, 128C and 128K to later-described developing devices 193 of imaging units of corresponding colors 110Y, 110M, 110C and 110K.

The imaging units 110Y, 110M, 110C and 110K as image forming sections corresponding to respective color toners of yellow (Y), magenta (M), cyan (C) and black (K) are placed side by side in order from the left-hand side in the drawing below the intermediate transfer belt 108. These imaging units 110Y, 110M, 110C and 110K are detachably mounted on the main body of the image forming apparatus 100. An unshown door used for attachment and detachment of these imaging units 110Y, 110M, 110C and 110K is provided on the main body casing 101.

The respective imaging units 110Y, 110M, 110C and 110K have completely similar configuration except for a difference in toner color that the respective units handle. More specifically, the yellow imaging unit 110Y for example is integrally composed of a photoconductor drum 190, a charging device 191, an exposure device 192, a developing device 193 for development with use of toner, and a cleaning device 195. A primary transfer roller 194 is provided in a position facing the photoconductor drum 190 across the intermediate transfer belt 108. At the time of image formation, the surface of the photoconductor drum 190 is first uniformly charged by the charging device 191, and then the surface of the photoconductor drum 190 is exposed by the exposure device 192 in response to an image signal inputted from, for example, an unshown external unit to form a latent image thereon. Next, the latent image on the surface of the photoconductor drum 190 is developed into a toner image by the developing device 193. This toner image is transferred onto the intermediate transfer belt 108 upon voltage application to between the photoconductor drum 190 and the primary transfer roller 194. The transfer residual toner on the surface of the photoconductor drum 190 is cleaned by a cleaning device 195.

As the intermediate transfer belt 108 moves in the arrow X direction, overlapped toner images of four colors are formed on the intermediate transfer belt 108 by each of the imaging units 110Y, 110M, 110C and 110K.

Provided on the left-hand side of the intermediate transfer belt 108 are a cleaning device 125 for removing residual toner from the surface of the intermediate transfer belt 108 and a toner collecting box 126 for collecting the toner removed by the cleaning device 125. A secondary transfer roller 112 is provided on the right-hand side of the intermediate transfer belt 108 across a conveying path 124 for paper sheets. Conveying rollers 120 and 119 are provided respectively at positions corresponding to upstream and downstream sides of the secondary transfer roller 112 on the conveying path 124. It is to be noted that a photo sensor (toner concentration sensor) 115 for detecting a toner pattern on the intermediate transfer belt 108 is provided integrally with the conveying roller 120.

A fixing device 130 for fixing toner onto paper sheets is provided on the upper right part inside the main body casing 101. The fixing device 130 is composed of a paper feed sensor 116 as a paper sensor for detecting paper sheets as sheets conveyed into the fixing device 130, a heating roller 131 extending vertically with respect to the page of FIG. 2, and a pressure roller 132 as a pressure applying member also extending vertically with respect to the page of FIG. 2 and being in pressure contact with the heating roller 131. In this example, the heating roller 131 incorporates an unshown heating source. The pressure roller 132 is biased toward the heating roller 131 with an unshown spring. Accordingly, the heating roller 131 and the pressure roller 132 form a nip area N for fixation. As a sheet (e.g., paper sheet 90) carrying a toner image transferred thereon passes through the nip area N, the toner image is fixed onto the paper sheet 90. It is to be noted that the paper feed sensor 116 is provided upstream from the nip area N with respect to a sheet conveying direction. The fixing device 130 operates based on the timing of the paper feed sensor 116 detecting a sheet.

Paper cassettes 140 and 141 for respectively stocking paper sheets 90 and 91 as the sheets on which images are to be formed are provided in two levels below the imaging units 110Y, 110M, 110C and 110K within the main body casing 101. Feed rollers 150 and 151 are respectively attached to upper right portions of the paper cassettes 140 and 141 in the drawing. Paper sheets 90 are sent out from the upper-side paper cassette 140 to the conveying path 124 extending upwards one by one by the feed roller 150. Similarly, paper sheets 91 are sent out from the lower-side paper cassette 141 to the conveying path 124 extending upward one by one by the feed roller 151. It is to be noted that a part of the conveying path 124 (a portion generally facing the right ends of the paper cassettes 140, 141 and a later-described horizontal conveyance unit 148) is constituted of a conveyance door 145 which can be opened and closed with respect to the main body casing 101.

In a position corresponding to the lowermost part of the main body casing 101 below the paper cassette 141, a first sheet feeding stocker 142 for stocking paper sheets (hereinafter referred to as “left-side sheet feeding stocker”) and a second sheet feeding stocker 143 for stocking paper sheets 93 (hereinafter referred to as “right-side sheet feeding stocker”) are placed side by side in right and left directions in the drawing. In a position corresponding to a section directly above the right-side sheet feeding stocker 143, a horizontal conveyance unit 148 equipped with feed rollers 152 a and 152 b is provided separately from the left-side sheet feeding stocker 142 and the right-side sheet feeding stocker 143. In a position corresponding to the right-hand side of the right-side sheet feeding stocker 143, a sheet feeding unit 149 equipped with the feed rollers 153 a and 153 b is provided (the sheet feeding unit 149 is fixed to the main body casing 101). The paper sheets 92 are sent out from the left-side sheet feeding stocker 142 to the horizontal conveying path 117 formed by the horizontal conveyance unit 148 and then to the conveying path 124 extending upward one by one by the feed rollers 152 a and 152 b. The paper sheets 93 are sent out from the right-side paper cassette 143 to the conveying path 124 extending upwards one by one by the feed rollers 153 a and 153 b. It is to be noted that FIG. 3 shows the left-side sheet feeding stocker 142, the right-side sheet feeding stocker 143, the horizontal conveyance unit 148, and the sheet feeding unit 149 as the components of a sheet feeding device seen from the front side.

When the image forming apparatus 100 receives a print job from the outside for example, a control section 200 constituted of a CPU (Central Processing Unit) shown in FIG. 2 controls the entire image forming apparatus 100 to execute image forming operation according to the print job.

At the time of image formation, the paper sheets 92 are sent out by the feed rollers 152 a and 152 b from, for example, the left-side sheet feeding stocker 142 to the conveying path 124 extending upward one by one through the horizontal conveying path 117. The paper sheets 92 are then sent into a toner transfer position between the intermediate transfer belt 108 and the secondary transfer roller 112 by the conveying roller 120. Meanwhile, an overlapped toner image of four colors is formed on the intermediate transfer belt 108 by each of the imaging units 110Y, 110M, 110C and 110K as mentioned before. The toner image of four colors on the intermediate transfer belt 108 is transferred onto a paper sheet 92, which was sent into the above-mentioned toner transfer position, by the secondary transfer roller 112. The paper sheet 92 with the toner image transferred thereon receives heat and pressure while being conveyed through the nip area N formed between the heating roller 131 and the pressure roller 132 of the fixing unit 130. As a result, the toner image is fixed onto the paper sheet 92. The paper sheet 92 with the toner image fixed thereto is then discharged by a paper ejecting roller 121 into a paper ejection tray section 122 provided on the upper surface of the main body casing 101. It is to be noted that the same image forming operation applies when the paper sheets 90, 91, 93 are sent out to the conveying path 124 from the paper cassettes 140, 141 or the right-side sheet feeding stocker 143.

As shown in FIG. 1, the left-side sheet feeding stocker 142, the right-side sheet feeding stocker 143, and the horizontal conveyance unit 148 respectively have front doors 42, 43, and 48 integrally provided. The front doors 42, 43 and 48 have handles 42 a, 43 a and 48 a, respectively. These handles 42 a, 43 a and 48 a are used by users to pull out the left-side sheet feeding stocker 142, the right-side sheet feeding stocker 143 and the horizontal conveyance unit 148 from the main body casing 101 to the front side.

As shown in FIG. 4, a plate-like protrusion 48 p protruding to the left side is integrally provided at the left edge of the front door 48 of the horizontal conveyance unit 148. The protrusion 48 p of the front door 48 is structured to engage with a back side portion 42 b of the front door 42 of the left-side sheet feeding stocker 142 to function as an engaging mechanism (as described later). In FIG. 4, the left-side sheet feeding stocker 142 is in the state of being pulled out forward (in a direction shown with an arrow a) for the sake of graphic presentation.

As shown in FIG. 5, a protrusion 145 p in a shape of a quarter of a circle protruding to the left side and curved downward is integrally provided in the lower part of the conveyance door 145. The conveyance door 145 is attached to the main body casing 101 (see FIG. 1) by a hinge 146 so that it can be opened and closed with respect to the main body casing 101. When the conveyance door 145 is in the state of being closed with respect to the main body casing 101 (in the state where the conveyance door 145 stands perpendicularly as shown in FIG. 5), the protrusion 145 p of the conveyance door 145 engages with a front side portion 148 f of the horizontal conveyance unit 148 and functions as a locking mechanism for prohibiting the horizontal conveyance unit 148 from being pulled out forward from the main body casing 101. FIG. 6 shows the state corresponding to FIG. 5 as seen from a diagonally upward side. In the state where the conveyance door 145 is opened with respect to the main body casing 101 (in the state where the conveyance door 145 is inclined in a direction shown with an arrow c) as shown in FIG. 7, engagement between the protrusion 145 p of the conveyance door 145 and the front side portion 148 f of the horizontal conveyance unit 148 is canceled so that the horizontal conveyance unit 148 is permitted to be pulled out forward from the main body casing 101. Therefore, as shown in FIG. 8, users can pull out the horizontal conveyance unit 148 from the main body casing 101 to the front side (direction shown with an arrow b).

As described before, a plate-like protrusion 48 p protruding to the left side is integrally provided at the left edge of the front door 48 of the horizontal conveyance unit 148. Therefore, as seen from the above for example, in the state where the left-side and right-side sheet feeding stockers 142 and 143 and the horizontal conveyance unit 148 are housed in the main body as shown in FIG. 9A, the protrusion 48 p of the front door 48 of the horizontal conveyance unit 148 is in contact with the back side portion 42 b of the front door 42 of the left-side sheet feeding stocker 142. When users try to pull out the horizontal conveyance unit 148 to the front side (in the direction shown with the arrow b) in this state, the protrusion 48 p of the front door 48 of the horizontal conveyance unit 148 engages with the back side portion 42 b of the front door 42 of the left-side sheet feeding stocker 142 as shown in FIG. 9B, so that the left-side sheet feeding stocker 142 is pulled out integrally with the horizontal conveyance unit 148. It is to be noted that in FIG. 9B, stationary members are shaded for easy understanding.

In this image forming apparatus, the following operations are executed with respect to the sheet feeding device.

First, during operation of the image forming apparatus, the front doors 42, 43 and 48 are closed to the main body casing 101 so that the left-side sheet feeding stocker 142, the right-side sheet feeding stocker 143 and the horizontal conveyance unit 148 are in the state of being housed in the main body casing 101 as shown in FIG. 10. It is to be noted that in FIG. 10 and later-described FIG. 11, FIG. 12 and FIG. 13, a side panel of the main body casing 101 is omitted for easy understanding.

When users wish to restock the left-side sheet feeding stocker 142 with paper sheets, the users pull the handle 42 a of the front door 42 to the front side (in the direction shown with the arrow a) as shown in FIG. 11, and pull out the left-side sheet feeding stocker 142 forward from the main body casing 101. In this state, users can easily load paper sheets onto the left-side sheet feeding stocker 142.

Similarly, when users wish to restock the right-side sheet feeding stocker 143 with paper sheets, the users pull the handle 43 a of the front door 43 to the front side (in the direction shown with an arrow d) as shown in FIG. 12 and pull out the right-side sheet feeding stocker 143 forward from the main body casing 101. In this state, users can easily load paper sheets onto the right-side sheet feeding stocker 143.

It is to be noted that for restocking both the left-side and right-side sheet feeding stockers 142 and 143 with paper sheets at the same time, users pull handles 42 a and 43 a of the front doors 42 and 43 to the front side and pull out both the left-side and right-side sheet feeding stockers 142 and 143 forward from the main body casing 101. In this state, users can easily load paper sheets onto both the left-side and right-side sheet feeding stockers 142 and 143.

At the time of jamming relating to paper feed operation, it is predetermined as procedures of jam processing that the conveyance door 145 is first opened as shown in FIG. 7, and a jammed paper, if visible, is removed, or the horizontal conveyance unit 148 is pulled out forward if a jammed paper is invisible. Such procedures may be prescribed in a manual or may be presented to users by a device structured so that the procedures are displayed at the time of jam occurrence.

It is assumed herein that users try to pull out the horizontal conveyance unit 148 to the front side (in the direction shown with the arrow b) as shown in FIG. 13 according to the procedures of the jam processing prescribed by the manual. In this case, since the conveyance door 145 is opened with respect to the main body casing 101, engagement between the protrusion 145 p of the conveyance door 145 and the front side portion 148 f of the horizontal conveyance unit 148 is canceled so that the horizontal conveyance unit 148 is permitted to be pulled out forward from the main body casing 101 (see FIG. 7). Consequently, when users try to pull out the horizontal conveyance unit 148 to the front side (in the direction shown with the arrow b) in this state, the protrusion 48 p of the front door 48 of the horizontal conveyance unit 148 engages with the back side portion 48 b of the front door 42 of the left-side sheet feeding stocker 142 as shown in FIG. 13, so that the left-side sheet feeding stocker 142 is pulled out integrally with the horizontal conveyance unit 148. This enables users to easily remove jammed paper sheets while preventing paper sheet tear even when the paper sheets stop at a position lapping over both the left-side sheet feeding stocker 142 and the horizontal conveyance unit 148 at the time of jamming relating to paper feed operation.

Next, it is assumed that users try to pull out the horizontal conveyance unit 148 to the front side (in the direction shown with the arrow b) at the time other than jamming relating to paper feed operation (at the time of normal operation for example). In this case, since the conveyance door 145 is closed with respect to the main body casing 101, the protrusion 145 p of the conveyance door 145 engages with the front side portion 148 f of the horizontal conveyance unit 148 so that the horizontal conveyance unit 148 is prohibited from being pulled out forward from the main body casing 101. As a result, the horizontal conveyance unit 148 is prevented from being unnecessarily pulled out from the main body casing 101.

In the above-mentioned embodiment, the protrusion 145 p of the conveyance door 145 engages with or disengages from the front side portion 148 f of the horizontal conveyance unit 148 in response to opening and closing of the conveyance door 145 with respect to the main body casing 101, as a result of which pulling out the horizontal conveyance unit 148 from the main body casing 101 is permitted or prohibited (locked). Therefore, at the time of jamming relating to paper feed operation, users can unconsciously cancel locking mechanism (145 p, 148 f) with respect to the horizontal conveyance unit 148.

It should be understood that the sheet feeding device of the invention is widely applicable not only to image forming apparatuses but also to various equipment having a conveyance system similar to that in the image forming apparatus 100.

As is described above, a sheet feeding device in one aspect of the present invention comprises:

first and second sheet feeding stockers provided in a main body and placed side by side in a horizontal direction, wherein

sheets are taken out from the first sheet feeding stocker and conveyed through a horizontal conveyance unit provided above the second sheet feeding stocker, wherein

the respective first and second sheet feeding stockers can independently be pulled out forward from the main body in a direction intersecting with a sheet conveying direction in the horizontal conveyance unit, and wherein

an engaging mechanism is provided for engaging the horizontal conveyance unit and the first sheet feeding stocker so that the first sheet feeding stocker is pulled out integrally with the horizontal conveyance unit when the horizontal conveyance unit is pulled out forward from the main body.

In this sheet feeding device, the respective first and second sheet feeding stockers can independently be pulled out forward from the main body in a direction intersecting with a sheet conveying direction in the horizontal conveyance unit. Therefore, for restocking paper sheets, users can easily load sheets onto the first and second sheet feeding stockers in the state where the respective first and second sheet feeding stockers are pulled out independently or both of them are pulled out forward from the main body. At the time of jamming relating to paper feed operation, users are assumed to pull out the horizontal conveyance unit forward from the main body. In that case, an engaging mechanism engages the horizontal conveyance unit and the first sheet feeding stocker so that the first sheet feeding stocker is pulled out integrally with the horizontal conveyance unit. This enables users to easily remove jammed paper sheets while preventing paper sheet tear even when the paper sheets stop at a position lapping over both the first sheet feeding stocker and the horizontal conveyance unit at the time of jamming relating to paper feed operation.

In the sheet feeding device of one embodiment, the engaging mechanism includes a protrusion protruding horizontally from an edge of a front door of the horizontal conveyance unit so as to overlap with a back side portion of a front door of the first sheet feeding stocker.

The sheet feeding device of one embodiment comprises a locking mechanism which permits the horizontal conveyance unit to be pulled out forward from the main body at a time of jamming relating to paper feed operation while prohibiting the horizontal conveyance unit from being pulled out forward from the main body at a time other than jamming relating to paper feed operation.

In the sheet feeding device of this one embodiment, the horizontal conveyance unit is permitted to be pulled out forward from the main body at the time of jamming relating to paper feed operation. Therefore, users can easily pull out the horizontal conveyance unit forward from the main body together with the first sheet feeding stocker. As a result, users can easily remove jammed sheets while preventing sheet tear as mentioned before. At the time other than jamming relating to paper feed operation, the horizontal conveyance unit is prohibited from being pulled out forward from the main body by the locking mechanism. As a consequence, the horizontal conveyance unit is prevented from being unnecessarily pulled out from the main body.

The sheet feeding device of one embodiment comprises:

a door which can be opened and closed with respect to the main body, the door being provided in a region of a lateral surface of the main body which faces an end portion of the horizontal conveyance unit, wherein

the locking mechanism executes permitting or prohibiting operation according to opening and closing of the door with respect to the main body.

At the time of jamming relating to paper feed operation, jammed sheets tend to exist in a region of the lateral surface of the main body which faces an end portion of the horizontal conveyance unit. Accordingly, a door which can be opened and closed with respect to the main body is generally provided in this region to facilitate jam processing. At the time of jam processing, users first open the door, find out a jammed sheet, and try to remove the sheet. In this regard, in the sheet feeding device of this one embodiment, the locking mechanism executes permitting or prohibiting operation according to opening and closing of the door with respect to the main body. Therefore, when the door is opened with respect to the main body for jam processing, the horizontal conveyance unit is permitted to be pulled out forward from the main body. As a result, users can easily remove a jammed sheet while preventing sheet tear as mentioned before. At the time other than jamming relating to paper feed operation, the door is closed with respect to the main body, so that the locking mechanism prohibits the horizontal conveyance unit from being pulled out forward from the main body. As a consequence, the horizontal conveyance unit is prevented from being unnecessarily pulled out from the main body as described before. With this configuration, users can unconsciously unlock the locking mechanism at the time of jamming relating to paper feed operation.

It is to be noted that the door should preferably constitute a part of the conveying path for conveying the sheets.

In the sheet feeding device of one embodiment, the locking mechanism includes a protrusion which can engage with a front side portion of the horizontal conveyance unit, the locking mechanism being provided in the region of the lateral surface of the main body which faces the end portion of the horizontal conveyance unit.

In the sheet feeding device of one embodiment, the protrusion has a circular arc shape horizontally protruding from the region and curved downward.

An image forming apparatus in one aspect of the present invention comprises the sheet feeding device.

The image forming apparatus has the sheet feeding device, which enables users to easily remove jammed sheets while preventing sheet tear at the time of jamming relating to paper feed operation.

As is clear from the above, according to the sheet feeding device or the image forming apparatus of the invention, users can easily remove jammed sheets while preventing sheet tear at the time of jamming relating to paper feed operation.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. 

1. A sheet feeding device, comprising: first and second sheet feeding stockers provided in a main body and placed side by side in a horizontal direction, wherein sheets are taken out from the first sheet feeding stocker and conveyed through a horizontal conveyance unit provided above the second sheet feeding stocker, wherein the respective first and second sheet feeding stockers can independently be pulled out forward from the main body in a direction intersecting with a sheet conveying direction in the horizontal conveyance unit, and wherein an engaging mechanism is provided for engaging the horizontal conveyance unit and the first sheet feeding stocker so that the first sheet feeding stocker is pulled out integrally with the horizontal conveyance unit when the horizontal conveyance unit is pulled out forward from the main body.
 2. The sheet feeding device as claimed in claim 1, wherein the engaging mechanism includes a protrusion protruding horizontally from an edge of a front door of the horizontal conveyance unit so as to overlap with a back side portion of a front door of the first sheet feeding stocker.
 3. The sheet feeding device as claimed in claim 1, comprising: a locking mechanism which permits the horizontal conveyance unit to be pulled out forward from the main body at a time of jamming relating to paper feed operation while prohibiting the horizontal conveyance unit from being pulled out forward from the main body at a time other than jamming relating to paper feed operation.
 4. The sheet feeding device as claimed in claim 3, comprising: a door which can be opened and closed with respect to the main body, the door being provided in a region of a lateral surface of the main body which faces an end portion of the horizontal conveyance unit, wherein the locking mechanism executes permitting or prohibiting operation according to opening and closing of the door with respect to the main body.
 5. The sheet feeding device as claimed in claim 3, wherein the locking mechanism includes a protrusion which can engage with a front side portion of the horizontal conveyance unit, the locking mechanism being provided in the region of the lateral surface of the main body which faces the end portion of the horizontal conveyance unit.
 6. The sheet feeding device as claimed in claim 5, wherein the protrusion has a circular arc shape horizontally protruding from the region and curved downward.
 7. An image forming apparatus comprising the sheet feeding device as claimed in claim
 1. 